This invention relates to security systems and more particularly to magnetically actuated sensor arrangements for monitoring door or window openings or the like as a part of an electrically monitored physical security system.
In high security applications, reed switches are commonly used, and in previously known devices (for example, U.S. Pat. No. 4,210,889), balanced magnetically biased reed switches were assembled in a predetermined configuration, so that a deception of the device by the manipulation of outside magnets becomes difficult. However, magnetically biased high security switches have disadvantages that due to changes in the magnetic strength of the biasing magnets, and due to their inherent sensitivity, they may malfunction and cause false alarms. Furthermore, magnetically balanced switches are difficult to manufacture and are costly because the magnets must be magnetically balanced carefully, either during installation, or as preset at the factory.